1. Field of Invention
The present invention relates to a method for operating a system of readers and, more particularly, to a method for operating a system of readers with an exchange mechanism.
2. Related Prior Art
Radio frequency identification (“RFID”) is used in various fields. RFID is a non-contact automatic identification technique based on transmission of radio for carrying data. With RFID, a large amount of data can be identified in a short period of time. Hence, for automatic control of vehicles, persons and cargo in airports, RFID is often used instead of the barcode identification technique. RFID has accomplished what other identification techniques cannot. Unlike the barcode identification technique, RFID does not require contact of a reader with a tag or alignment of the reader with the target tag. In addition, the tags used in RFID are less vulnerable to contaminants than the tags used in the barcode identification technique. Furthermore, there is more flexibility in locating the tags used in RFID than the barcode identification technique. For example, a tag used in RFID can be sandwiched between two layers of paper of a box.
RFID is based on inductive coupling or propagation coupling. In an RFID system, a tag is attached to an object by adhesion, insertion, hanging or implanting. As the object is located in a proper reading range around a reader, in a non-contact manner, the tag provides the reader with data such as an ID number. The data are decoded in the reader. The decoded data are sent to another apparatus for further processing.
Referring to FIG. 1, a typical RFID system includes a reader 11, a tag 12 and an antenna 13. The reader 11 sends a signal to the tag 12 so that the reader 11 actuates and recharges the tag 12 in an electro-magnetic field. Recharged, the tag 12 transmits data to the reader 11. The read 11 decodes the data and broadcasts the decoded data via the antenna 13. A processor such as a computer receives the decoded data and takes actions according to the decoded data.
RFID systems can be classified into low frequency systems (“LF”) operated at 125 KHz, high frequency systems (“HF”) operated at about 13.56 MHz, ultra high frequency systems (“UHF”) operated at 900 MHz, and microwave systems operated at 2.4 GHz or 5.8 GHz. An RFID system may include a portable or stationary reader. A portable reader is often carried and used by a person in an inventory check. A stationary reader is often attached to a door or gate of a factory. The stationary reader is expected to be more reliable than the portable reader. However, the stationary reader might lose or damage the data because the power of the transmission of the radio drops or the efficiency of the operation of a processor located therein drops after a long period of service.
Currently, to use the RFID system for a long period, the stationary reader is equipped with a trigger. After the RFID system is turned on, the trigger begins to work. The trigger puts the reader in a standby mode if it does not detect any object. The trigger sends a signal to the reader if it detects an object. With the signal, the reader beings to search for, actuate, recharge and receive data from a tag. Then, the reader returns to the standby mode, and waits for another signal from the trigger. There however are problems with this arrangement. At first, the reading efficiency and range might decrease after a long period of service. Secondly, the abnormal operation of the reader might last too long to keep the data in the reader.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.